Unusual 'embroidery'

I saw this and couldn't resist telling you about it.

Researchers in Uppsala University have just finished restoring a 14th Century manuscript - so far, so normal. However, unlike most medieval books whose holes, rips and tears have simply been left, this one has been repaired at some point in history with beautiful buttonhole stitch darns in bright silk threads. How beautiful!

Also, interestingly, this is an example of the apocrypal statement that "black fabric rots because of the dye". All of the silk threads are fine, except the black ones which now disintegrates upon touch. Colour analysis has revealed that the black threads were dyed with iron sulphate and tannin. (And they are, even now, a remarkably pure, strong black colour.) However, the authors state that:

"The whole dyeing process is very acidic and if the wrong proportions of tannin and iron salt are used, sulphuric acid forms considerably accelerating the natural decomposition of the thread or material."

This implies that the disintegration of thread only occurs if the dying was done incorrectly. Also, note that it has taken 600 years for the thread to rot into this state. It is unclear what, if any, effect even an improperly created iron/tannin dye would have on thread or fabric within an individuals lifetime.